Tap changing transfer switch having series breaks

ABSTRACT

A tap-changing transfer switch for tapped regulating transformers is provided with switch means capable of forming series breaks in each of its load current carrying circuits. The transfer switch is further provided, in addition to switch-over resistors, with resistor means for equalizing the recovery voltage appearing across each of its series breaks. This is achieved without the provision of any auxiliary switching means for switching the voltage distribution resistors.

United States Patent 91 Breuer et al.

[4 1 Apr. 23, 1974 TAP CHANGING TRANSFER SWITCH HAVING SERIES BREAKS lnventors: Wolfgang Breuer; Alexander Bleibtreu, both of Regensburg, Germany Maschinenfabrik Reinhausen Gebruder Scheubeck K.G., Regensburg, Germany Filed: May 31, 1973 Appl. No.: 365,643

Assignee:

Foreign Application Priority Data June 20, 1972 Germany 2230008 US. Cl. 307/136, 323/435 R Int. Cl. 1101f 29/02 Field of Search 200/11 TC; 307/134, 135, 307/136; 323/435 R; 336/142 [56] References Cited UNITED STATES PATENTS 3,174,097 3/1965 Bleibtrau 307/136 X Primary Examiner-James R. Scott Assistant ExaminerM. Ginsburg Attorney, Agent, or FirmErwin Salzer [5 7] ABSTRACT 4 Claims, 6 Drawing Figures PATENTEDAPRZB 1574 3.806. 735

sum 2 or 2 FfiGA FIG.5 L] v L2 TAP CHANGING TRANSFER SWITCH HAVING SERIES BREAKS BACKGROUND OF THE INVENTION This invention refers to tap-changing transfer switches and more particularly tap-changing transfer switches of the Jansen type which include ohmic tapchanging resistors which are inserted into the load circuit during tap-changing operations, but are not inserted into the load circuit when the load current is continuously derived from one and the same tap of a tapped transformer winding. Tap changing transfer switches of the aforementioned kind are well known in the art and are described in considerable detail in US. Pat. No. 3,176,089 to A. Bleibtreu et al., Mar. 30, 1965 for LOAD TAP CHANGERS FOR TRANSFORMERS and reference may be had to this patent for details of Jansen type transfer switches in general which details have no immediate bearing on the present invention.

An invention closely related to the present invention is disclosed in the copending patent application Ser. No. 365,642 filed May 31, 1973 of Wolfgang Breuer et al.

A tap changing regulating transformer includes the three following units: (a) a tapped transformer winding; (b) a transfer switch proper for switching load currents including overload currents; and (c) a selector switch interposed between the tapped transformer winding for selecting the pair of taps between which a tap-changing operation is to be performed. This invention can be fully understood without reference to the selector switch circuitry, and a consideration of its presence has, therefore, been deleted below. It may be mentioned, however, that transfer switches and the way in which such switches are associated with a transformer winding and with a transfer switch proper is disclosed in the above referred to patent to A. Bleibtreu et al.

As the voltage of tapped regulating transformers and the power thereof increased, it became necessary, or desirable, to substitute in J ansen-type transfer switches for each switching means having a pair of separable contacts serially arranged switching means capable of forming series breaks when their contacts are separated, or in the open positions thereof. Another reason for adopting series-break-forming switching means in J ansen-type transfer switches resides in the fact that the voltage between contiguous taps of a tapped transformer winding tends to increase whenever it is desired to cover a relatively large voltage range with a minimum of taps.

The fact that single break contact arrangements must often be replaced by series break contact arrangements gave rise to the problem of controlling the voltage distribution in transfer switches so as to substantially equalize the voltage appearing across each of a plurality of series breaks.

In the past such equalization has been achieved by means of special potential control resistors, and by utilizing the switchover resistors of Jansen-type transfer switches for voltage distribution purposes. Prior art transfer switches involving potential controls for series breaks require separate or additional control switches for establishing the required potential control circuits. This is a very serious drawback because these switches greatly increase the bulk and the complexity of the transfer switch proper, and require additional operating means and means for timing their operation. In addition thereto such separate or additional control switches must be designed to withstand the high voltages present in transfer switches of the kind under consideration.

It is the primary object of this invention to provide transfer switches for tap-changing transformers wherein each path of the load current is provided with switching means, or separable contact means, forming series breaks upon opening thereof, wherein the voltage across all these breaks is controlled in such a fashion that the voltage across each of a plurality of series breaks is substantially equal, and wherein these ends are achieved without resorting to separate or additional voltage control switches which must be opened in predetermined sequences.

SUMMARY OF THE INVENTION Transfer switches embodying this invention include means establishing a first load current branch extending from a first transformer winding tap to a load, and means establishing a second load current branch extending from a second transformer winding tap to said load.

Each said first load current branch and said second load current branch includes a main current path and an auxiliary current path parallel to said main current path. Said main current path and said auxiliary current path of each said first and second load current branch are provided with at least two serially arranged switch means having relatively movable contacts forming series breaks in the open positions thereof. The auxiliary current path of said first and said second load current branch each include a switch-over resistor conductively interconnecting said serially arranged switch means therein.

The transfer switches further include a pair of potential control resistors for controlling the potential distribution in said main current path of said first and said second load current branch. Each of said pair of potential control resistors conductively interconnects one point situated between two of said serially arranged switch means in said main current path with one resistor tap situated between the ends of said switch-over resistor.

Transfer switches embodying this invention include further an additional potential control resistor for controlling the potential distribution in said auxiliary current path of said first and second load current branch. Said additional control resistor and one of said switch means in said auxiliary current path of said first and said second load current branch form a direct conductive connection between the tap end of said first load current branch and the tap end of said second load current branch.

BRIEF DESCRIPTION OF'THE DRAWINGS FIG. 1 is a diagrammatic representation of a tapchanging transfer switch embodying the present invention, FIG. 1 showing the switch in one of its two limit positions;

FIG. 2 shows the same switch as FIG. 1 and in the same fashion as FIG. 1 and shows the constituent parts thereof in a first intermediate position between its two limit positions;

FIG. 3 shows the same switch as FIG. 1 in the same fashion as FIG. 1 and shows the constituent parts thereof in a second intermediate position between its two limit positions;

FIG. 4 shows the same switch as FIG. 1 in the same fashion as FIG. 1 and shows the constituent parts thereof in a third intermediate position between its two limit positions; I

FIG. 5 shows the same switch as FIG. 1 in the same fashion as FIG. 1 and shows the constituent parts thereof in the other of its two limit position; and

FIG. 6 shows a modification of the switch shown in FIGS. l-S, inclusive, in the same fashion as FIGS. 1-5 in a position other than any of its normal operating positions, i.e., with all its constituent contact means being open and forming breaks therebetween.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, and more particularly to FIGS. 1-5 thereof, reference characters U, and U, have been applied to indicate two contiguous taps of a tapped transformer winding. In the first stationary or limit position of the transfer switch shown in FIG. 1 the load current derived from tap U, flows from that tap by way of load current branch L, to a load not shown. In the second stationary or limit position of the transfer switch the load current is derived from tap U, and flows from that tap by way of load current branch L, to a load not shown. Load current branch L, includes the main current path I and the auxiliary current path III arranged parallel to the main current path I. In a like fashion load current branch L, includes the main current path II and the auxiliary current path IV arranged parallel to the main current path II. The main current path I is provided with at least two serially connected main switch means I, and I, having relatively movable contacts and forming series breaks in the open positions thereof. In like fashion the main current path II of load current branch L, is provided with at least two serially connected main switch means II, and II, having relatively movable contacts and forming series breaks in the open positions thereof. The auxiliary current path III is provided with at least two serially connected auxiliary switch means III, and III, having relatively movable contacts and forming series breaks in the open positions thereof. In like fashion the auxiliary current path IV is provided with at least two serially connected auxiliary switch means IV, and IV, having relatively movable contacts and forming series breaks in the open positions thereof. Reference characters R, and R, have been applied to indicate a pair of switch-over resistors, or tap-changing resistors, which are inserted into the load circuit when performing a tap-changing operation from tap U, to tap U,, or from tap U, to tap U,. Resistor R, is subdivided into two serially connected resistor portions R,, and R,, and a tap is formed between the two resistor portions R,, and R,,. In like fashion switchover or tap-changing resistor R, is subdivided into two resistor portions R and R,,, and a tap is formed between resistor portions R,, and R,,. The tap formed between resistor portions R,, and R,, is conductively connected by means of potential control resistor R to a point of main current path I situated between switch means I, and 1,. In like fashion the tap formed between resistor portions R and R,, is conductively connected by means of potential control resistor R, to a point of main current path II situated between switch means II, and II,. Reference character R, has been applied to indicate an additional potential control resistor. This resistor R, is provided for controlling the potential distribution in auxiliary current paths III and IV. Resistor R, and switch means III, and IV,, when closed, form a direct conductive connection between taps U, and U, or, in other words, resistor R and switch means III, and IV,, when closed, form a direct conductive connection between the tap-end of load current branch L, and the tap-end of load current branch L,. Resistor R, has a high ohmic value so that the current flowing directly from tap U, to tap U, or vice versa through circuit elements III,,R and IV, is quite small.

Switch means I, and I, are supposed to open and to close simultaneously, and to this end they may be tied together mechanically as indicated in the drawings by a dotted line. The same applies as to the pairs of switch means III,,III, and to the pair of switch means IV,,IV, and to the pair of switch means II,,II,. This has also been indicated in the drawings by dotted lines interconnecting switch means opened and closed simultaneously.

In the position of parts shown in FIG. I the entire load current is derived from tap U, and flows through first current branch L, and the two serially connected switch means or switches I, and I, arranged in main current path I. Switch means III,,III,,IV,,IV, and II,,II, are open, or separated, and therefore no current flows through auxiliary current paths III and IV and through main current path II.

The first step in performing a tap-changing operation from tap U, to tap U, consists in simultaneously closing auxiliary switch means III, and III, in auxiliary current path III, and shortly thereafter simultaneously opening main switch means I, and I, in main current path I. This position of parts is shown in FIG. 2. Closing of switch means III, and III, results in a voltage drop across resistor R,. That voltage drop is used along with the voltage drop along potential resistor R, for controlling or equalizing the potential across main switch means I, and I,. When the latter switch means open an arc may be formed across each of the resulting breaks, but such arcs extinguish at the first current zero. Now the entire load current is carried by auxiliary current path III and auxiliary switches III, and III, and the current is then limited by the insertion of resistor R, into the aforementioned current path.

The next step in performing a tap-changing operation from tap U, to tap U, consists in closing the two auxiliary switch means IV, and IV, in auxiliary current path IV, resulting in the position of parts shown in FIG. 3. In that position there is, in addition to the flow of the load current to the load not shown a flow of a circulat ing current from tap U, through resistor R, and switch means III, and III, and resistor R, and switch means IV, and IV, to tap U The magnitude of that circulating current is limited by the sum of resistors R, and R,. In addition to the above circulating current there is another circulating current whose path extends from tap U, through switch means III,, resistor R, and switch means IV, to tap U,. This circulating current is minimal on account of the magnitude of resistor R,.

The next step in performing a tap-changing operation from tap U, to tap U, consists in interrupting the auxiliary current path III by simultaneously opening switch means III, and III,. This results in the position of parts shown in FIG. 4. Forming of breaks at III, and III, may result in the formation of arcs at these breaks, but these arcs are short-lived and extinguish at the first current zero. When the switch means III, and III, open, a recovery voltage appears across the separated contacts thereof. The recovery voltage across the separated contacts of switch means III, corresponds to the voltage drop across switch-over resistor R The magnitude of switch-over resistor R, may be determined in such a way that the voltage drop along switch-over resistor R is equal to the voltage normally prevailing between contiguous taps U, and U The recovery voltage appearing across the separated contacts of switch means III, is equal to the difference in potential taps U, and U since the portion of the transformer winding between taps U, and U closed switch means IV, and resistor R is connected across the break formed by the separated contacts of switch means III Hence the recovery voltage is evenly distributed across the two series breaks formed by auxiliary switch means III, and III,.

The next step in performing a tap-changing operation from tap U, to tap U consists in simultaneously closing the main contact means II, and II,. This establishes a direct current path from tap U, to the load (not shown). Thereafter auxiliary switch means IV, and IV, are opened simultaneously. No arcing occurs when these switch means are opened since the current path II forms a very low resistance shunt across the current path IV. Opening of contact means IV, and [V terminates the tap-changing operation from tap U, to tap U The second limit position of the transfer switch which is established when the entire load current is derived only from tap U, is shown in FIG. 5.

It will be noted from the above that the transfer switch does not require any additional switch means for the control of the recovery voltage across its four pairs of switch means I, and 1,; II, and II,, III, and III, and IV, and W i.e., it does not require any additional switch means for switching either of the potential control resistors R ,R., and R The circuitry of FIG. 6 is intended for applications where tap-changing operations must be performed during protracted periods of overload. In FIG. 6 the same reference characters as in FIGS. 1 to 5, inclusive, have been applied to indicate like parts. Hence FIG. 6 calls for a description of such features only which differ from those shown in FIGS. 1 to 5. The transfer switch of FIG. 6 differs from the previously described transfer switch on account of the fact that an additional switchover resistor section R,;, is inserted between resistor section R and switch means "I and in that an additional switch-over resistor section R is inserted between resistor section R and switch means IV In other words, resistor R, is sub-divided into three sections R ,,,R,,, and R,,, and resistor R is sub-divided into three sections R ,,R and R When during a tapchanging operation switches IV, and IV, are in the closed and switches III, and III, in the open positions thereof, one portion of the total voltage drop across switch-over resistor R appears as recovery voltage across the separated contacts of switch means III, and another portion of said voltage drop is subtracted from or added to the voltage between taps U, and U, which appears as recovery voltage across the separated contacts of switch means III By appropriately subdividing switch-over resistors R, and R, into three sections, or by assigning appropriate ohmic values to the switch-over resistor sections R and R,;, and R and R respectively, the transfer switch may be endowed with the ability of equally distributing the recovery voltage appearing across auxiliary switch means III, and III,, or auxiliary switch means IV, and [V respectively, in various overload conditions.

The tap-changing operation from tap U to tap U, does not need to be described since the consecutive steps involved in this operation are apparent from what has been described above.

It will be apparent from the above that systems embodying the present invention include a tapped transformer winding having a first tap U, and a contiguous second tap U Such systems further include a first load current branch L, for conductively connecting said first tap U, to a load, and a second load current branch L, for conductively connecting said second tap U, to a load. Each said first load current branch L, and said second load current branch L, include a main current path I and II, and an auxiliary path III and IV parallel to said main current path. Systems embodying this invention further include two pairs of jointly movable main switch means I,,I and II,,II having relatively movable contacts. One pair I,,I of said two pairs of main switch means I,,I,;II,,II is arranged in series in said main current path I of said first load current branch L, and form series breaks in the open positions thereof. The other pair II,,II, of said main switch means is arranged in series in the main current path II of said second load current branch L, and forms series breaks in the open positions thereof.

Systems embodying this invention further include two pairs of jointly movable auxiliary switch means III,,III and IV,,IV having relatively movable contacts. One pair III,,III of said two pairs of auxiliary switch means III,,III ;IV,,IV is arranged in series in said auxiliary current path III of said first load current branch L, and forms series breaks in the open positions thereof. The other pair IV,,IV, of said two pairs of auxiliary switch means III,,III and IV,,IV is arranged in series in the auxiliary current path IV of said second load current branch L, and forms series breaks in the open positions thereof.

Systems embodying this invention further include a pair of switch-over resistors R,,R,. One of said pair of switch-over resistors R,,R is interposed between said one pair III,,III, of said two pairs III,,III and IV,,IV, of auxiliary switch means and the other of said two pairs of switch-over resistors R,,R is interposed between said other pair IV,,IV of said two pairs III,,III, and IV,,IV of auxiliary switch means.

Systems embodying this invention further include a pair of potential control resistors R ,R for controlling the potential distribution in said main current path I of said first'load current branch L, and in said main current path II of said second load current branch L,. One of said potential control resistors R.,,R conductively interconnects one point of said one of said pair of switch-over resistors R,,R, situated between the ends thereof with one point situated between said one pair I,,I of said pairs of main switch means I,,I and II,,II

The other of said pair of potential control resistors R,,R conductively interconnects one point of said other of said pair of switch-over resistors R,,R situated between the ends thereof with one point situated between said other pair II,,II of said two pairs I,,I, and II,,II of main switch means.

Systems embodying this invention further include an additional potential control resistor R for controlling the potential distribution of said auxiliary current path III of said first load current branch L and in said auxiliary current path IV of said second load current branch L Said additional potential control resistor R forms part of an additional current path extending from said first tap U, to said second tap U The aforementioned additional current path includes one of said auxiliary switch means H1 in said auxiliary current path III of said first load current branch L said additional control resistor R and one of said auxiliary switch means [V in said auxiliary current path IV of said second load current branch L We claim as our invention: 1. A tap-changing transfer switch having series breaks comprising in combination:

a. means establishing a first load current branch from a first transformer winding tap to a load; b. means establishing a second load current branch from a second transformer winding tap to said load;

c. each said first load current branch and said second load current branch including a main current path and an auxiliary current path parallel to said main current path, each said main current path and said auxiliary current path being provided with at least two serially arranged switch means having relatively movable contacts forming series breaks in the open positions thereof, and said auxiliary current path of said first and second load current branch each including a switch-over resistor conductively interconnecting two of said serially arranged switch means therein;

d. a pair of potential control resistors for controlling the potential distribution in said main current path of said first and of said second load current branch, each of said pair of potential control resistors conductively interconnecting one point situated between two of said serially arranged switch means in said main current path with one resistor tap situated between the ends of said switch-over resistor; and

e. an additional potential control resistor for controlling the potential distribution in said auxiliary current path of said first and second load current branch, said additional potential control resistor and one of said switch means in said auxiliary current path of said first and said second load current branch forming a direct conductive connection between the tap end of said first load current branch and the tap end of said second load current branch.

2. A tap-changing transfer switch as specified in claim I wherein said direct conductive connection between said tap end of said first load current branch and said tap end of said second load current branch includes a portion of said switch-over resistor in said auxiliary current path of said first and said second load current branch.

3. In combination a. a tapped transformer winding having a first tap and a contiguous second tap;

b. a first load current branch for conductively connecting said first tap to a load, and a second load current branch for conductively connecting said second tap to said load;

c. each said first load current branch and said second load current branch including a main current path and an auxiliary current path parallel to said main current path;

(1. two pairs of jointly movable main switch means having relatively movable contacts, one pair of said two pairs of main switch means being arranged in series in said main current path of said first load current branch and forming series breaks in the open positions thereof and the other pair of said two pairs of main switch means being arranged in series in the main current path of said second load current branch and forming series breaks in the open positions thereof;

e. two pairs of jointly movable auxiliary switch means having relatively movable contacts, one pair of said two pairs of auxiliary switch means being arranged in series in said auxiliary current path of said first load current branch and forming series breaks in the open positions thereof, and the other pair of said two pairs of auxiliary switch means being arranged in series in the auxiliary current path of said second load current branch and forming series breaks in the open positions thereof;

f. a pair of switch-over resistors, one of said pair of switch-over resistors being interposed between said one pair of said two pairs of auxiliary switch means and the other of said pair of switch-over resistors being interposed between said other of said two pairs of auxiliary switch means;

g. a pair of potential control resistors for controlling the potential distribution in said main current path of said first load current branch and in said main current path of said second load current branch, one of said pair of potential control resistors conductively interconnecting one point of said one of said pair of switch-over resistors situated between the ends thereof with one point situated between said one pair of said two pairs of main switch means, and the other of said pair of potential control resistors conductively interconnecting one point of said other of said pair of switch-over resistors situated between the ends thereof with one point situated between said other pair of said two pairs of main switch means; and

. an additional potential control resistor for controlling the potential distribution in said auxiliary current path of said first load current branch and in said auxiliary current path of said second load current branch, said additional potential control resistor forming part of an additional current path extending from said first tap to said second tap and including one of said auxiliary switch means in said auxiliary current path of said first load current branch, said additional potential control resistor and one of said auxiliary switch means in said auxiliary current path of said second load current branch.

4. A system as specified in claim 3 wherein said additional current path includes a portion of each said pair of switch-over resistors. 

1. A tap-changing transfer switch having series breaks comprising in combination: a. means establishing a first load current branch from a first transformer winding tap to a load; b. means establishing a second load current branch from a second transformer winding tap to said load; c. each said first load current branch and said second load current branch including a main current path and an auxiliary current path parallel to said main current path, each said main current path and said auxiliary current path being provided with at least two serially arranged switch means having relatively movable contacts forming series breaks in the open positions thereof, and said auxiliary current path of said first and second load current branch each including a switchover resistor conductively interconnecting two of said serially arranged switch means therein; d. a pair of potential control resistors for controlling the potential distribution in said main current path of said first and of said second load current branch, each of said pair of potential control resistors conductively interconnecting one point situated between two of said serially arranged switch means in said main current path with one resistor tap situated between the ends of said switch-over resistor; and e. an additional potential control resistor for controlling the potential distribution in said auxiliary current path of said first and second load current branch, said additional potential control resistor and one of said switch means in said auxiliary current path of said first and said second load current branch forming a direct conductive connection between the tap end of said first load current branch and the tap end of said second load current branch.
 2. A tap-changing transfer switch as specified in claim 1 wherein said direct conductive connection between said tap end of said first load current branch and said tap end of said second load current branch includes a portion of said switch-over resistor in said auxiliary current path of said first and said second load current branch.
 3. In combination a. a tapped transformer winding having a first tap and a contiguous second tap; b. a first load current branch for conductively connecting said first tap to a load, and a second load current branch for conductively connecting said second tap to said load; c. each said first load current branch and said second load current branch including a main current path and an auxiliary current path parallel to said main current path; d. two pairs of jointly movable main switch means having relatively movable contacts, one pair of said two pairs of main switch means being arranged in series in said main current path of said first load current branch and forming series breaks in the open positions thereof and the other pair of said two pairs of main switch means being arranged in series in the main current path of said second load current branch and forming series breaks in the open positions thereof; e. two pairs of jointly movable auxiliary switch means having relatively movable contacts, one pair of said two pairs of auxiliary switch means being arranged in series in said auxiliary current path oF said first load current branch and forming series breaks in the open positions thereof, and the other pair of said two pairs of auxiliary switch means being arranged in series in the auxiliary current path of said second load current branch and forming series breaks in the open positions thereof; f. a pair of switch-over resistors, one of said pair of switch-over resistors being interposed between said one pair of said two pairs of auxiliary switch means and the other of said pair of switch-over resistors being interposed between said other of said two pairs of auxiliary switch means; g. a pair of potential control resistors for controlling the potential distribution in said main current path of said first load current branch and in said main current path of said second load current branch, one of said pair of potential control resistors conductively interconnecting one point of said one of said pair of switch-over resistors situated between the ends thereof with one point situated between said one pair of said two pairs of main switch means, and the other of said pair of potential control resistors conductively interconnecting one point of said other of said pair of switch-over resistors situated between the ends thereof with one point situated between said other pair of said two pairs of main switch means; and h. an additional potential control resistor for controlling the potential distribution in said auxiliary current path of said first load current branch and in said auxiliary current path of said second load current branch, said additional potential control resistor forming part of an additional current path extending from said first tap to said second tap and including one of said auxiliary switch means in said auxiliary current path of said first load current branch, said additional potential control resistor and one of said auxiliary switch means in said auxiliary current path of said second load current branch.
 4. A system as specified in claim 3 wherein said additional current path includes a portion of each said pair of switch-over resistors. 